Two weeks after the upgrade von Android 4.1 to 4.2 my devices was updated to Android 4.2.1. There is no official statement about the bugfixes or changes in this version. The only information is the confirmation screen before the update:

The size of the update was only 1.1 MB. So it is not really suprising, that the kernel version for 4.2.1 is the same as for 4.2...After the update several applications hung and the Nexus 7 was not really responsive -> but after a additional reboot everything was fine again....